Vehicles, for example automotive vehicles, boats, railway cars, and other mobile equipment, have self-contained on-board electrical networks which, usually, are supplied with electrical energy from an alternator which is coupled either to the prime mover or to the wheels of the vehicle. The speeds of operation vary widely. The loading on the alternator can vary widely; and, further, due to the mobile operation, the temperature to which the alternator and the other components, and specifically a floating battery is subjected, also can vary widely. Voltage regulators are customarily connected to the alternator to control the field current therethrough to maintain the output voltage at an approximately constant level. The field current is so controlled, typically by on-off control by mechanical or solid-state voltage regulators, to maintain an average current through the exciter or field winding of the alternator for at least approximately constant voltage output.
Automotive-type vehicles, particularly those operating in cold winter operations, are subjected to special requirements. Under cold winter conditions, the inner resistance of the battery connected to the on-board vehicular network increases appreciably. The cold starting power available from the battery thus drops rapidly, and battery charge problems result, especially at low engine speeds. This difficulty is increased if the vehicle is used in urban traffic, that is, under conditions under which the engine does not operate at higher speeds. Some equipment to which the vehicle is connected cannot tolerate over-voltages; excessive voltages are extremely damaging to a battery, and may destroy transitorized on-board equipment. Battery charging problems, particularly upon low operating engine speed, and especially when coupled with low temperatures, arise, and, in order to meet requirements, the design of the on-board vehicular network usually is a compromise between the requirements of sufficient battery charge on the one hand, and, on the other, maintenance of a maximum voltage below that which might cause damage to voltage-sensitive equipment installed in the vehicle. This compromise results in inefficient energy balance in operation of the alternator. In city traffic, the power reserve available from the alternator may be marginal and, under excessive city operating conditions, the battery may gradually discharge. Yet, the generator, due to its winding capacity and wiring layout, is capable of substantially higher power output since it is capable of supplying more power at sustained higher voltage operation.